The present invention relates generally to a screw coupling safety mechanism.
In screw pipe couplings, a number of safety systems have been used in order to prevent an unintentional loosening of the sleeve nuts. One known method for preventing loosening of nuts is to drill a bore in the nuts and lock the nuts by means of a twisted safety wire. This method has the disadvantages that it is expensive and there is no possibility of checking whether the safety wire has been overextended by the twisting. Overextending the wire can cause breakage of the wire when the coupling is subjected to vibrations.
Another known device for securing screw pipe couplings consists of a preformed knife edge ring and a conical ring which are pressed into a tube collar when pulling on the sleeve nut (as shown for example in Ermeto Main Catalog 105/1974, Edition 3/76). The disadvantage of this safety system is that leakages can appear as a result of thermal expansions or vibrations in the pipelines. Further, this safety mechanism is expensive since a great number of knife edge rings, conical rings and tapered bushings have to be kept on hand for different pipe diameters.
It is therefore an object of the present invention to provide a screw coupling safety mechanism which can be used several times and which can be easily and cheaply produced.
The abovementioned object and others are realized in accordance with the present invention by providing a safety mechanism comprising a first toothed disk and a second toothed disk with the same outside diameter. The inner circumference of the first toothed disk includes safety catches arranged for locking the first disk in position. The inner circumference of the second toothed disk includes safety catches arranged for locking the second disk in position and retaining springs for maintaining separation between the disks. By the arrangement of one disk having safety catches and retaining springs on the inner circumference, it is possible to preserve the separation between the two toothed disks by a simple bending of the retaining springs. Also, the safety catches provided on the inner circumference of both toothed disks allow each of the disks to be locked in position on screwed nuts or on a flattened slot of a round nut.
According to a further feature of the present invention one disk is provided with an even number of teeth and the other an uneven number of teeth. With the different number of teeth on each toothed disk, for example 12 teeth on one and 11 teeth on the second disk, it is possible to more easily align and bend one tooth of one disk into a gap formed between two teeth of the second disk for every setting of the tightened nut. Since the safety catches on each disk lie against the hexagon head of a screwed nut or on a flattened-out pipe section to lock each disk against rotation, the bending of the tooth produces a locked safety mechanism.
In a preferred embodiment each toothed disk features at least two safety catches and the second of the two toothed disks additionally includes at least four safety springs. This arrangement of safety catches and retaining springs on the two toothed disks, in addition to providing satisfactory centering, also establishes a uniform separation between the two toothed disks over the entire circumference of the disks.
According to a further feature of the preferred embodiment of the present invention, the safety catches and retaining springs are bent in mutually opposed directions to one toothed disk plane. The bending of the safety catches and retaining springs in the required direction is accomplished in a simple manner, for example, by punching in deflection curve bending lines into the disks.